The wildfire near Yosemite National Park is 20 percent contained, while more than 4,000 firefighters work towards quelling the huge blaze altogether. NBC's Tom Costello reports.

Regional forecasts

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>>>the massive wildfire burning near
yosemite national park
is growing this morning but some good news, crews are finally making progress. tom costello has the overnight developments, tom, good morning to you.

>>good morning. i'm going to speak softly because firefighters are sleeping around me here. they think they're getting the upper hand. containment at 20%. meanwhile they're monitoring the
water supply
and quality in
san francisco
because that city's water comes from a reservoir up here. meanwhile, thousands of homes are threatened right now and some have been lost.

>>oh, man.

>> reporter: 80-year-old lewis had his heart broken monday. 70 years ago his father built a family cabin on the doorstep to
yosemite national park
. on monday, he returned to find it was all gone.

>>this was the main cabin here. it all comes back to life and you remember back when your -- little kids, you know.

>> reporter: the fire
burning inside
the
national forest
and remote corner of yosemite is still out of control. the terrain is dangerous. steep, rugged and full of dry fuel.

>>i fought fire from alaska to florida, from new england to california, and this is one of the toughest fights i've ever faced.

>>the fire, if it comes in this direction will come north or south.

>> reporter: ron commands five engine companies watching over the
robin hood
road neighborhood. if the fire comes over the ridge, it could rain hot embers on the tree tops and the home.

>>this is not a bribe. they said they're going to be there all day. it's reassuring to have them there.

>> reporter: fighting the fire in the wilderness could take a long time.

>>we have explosive fuels out there unlike anything we have ever seen before.

>> reporter: the priority now is ensuring the safety of the 4,000 firefighters on the front lines.

>>fire commanders say that the brush and trees are so dry here, if you go to the lumber store and buy a 2 by 4, that wood would have twice as much moisture as what they're dealing with in the forest here.